Advancing the machinability and tribological characteristics of AISI 9310 steel using a novel ultrasonic vibration-assisted MQL approach

High production machining of low alloyed hardened steel AISI 9310 generates elevated cutting temperatures due to material's hardness and toughness causing dimensional deviations, premature failure of cutting tools, material softening, poor surface finish, rapid oxidation, and corrosion. This study proposes the implementation of an indigenously developed cooling and lubrication approach named ultrasonic atomization-based minimum quantity lubrication (UMQL) technique using eco-benign sunflower oil as a lubricant during finish milling, to control the cutting heat and to improve the machinability. To assess machinability of the AISI 9310 steel under UMQL, milling tests are carried out at varying machining parameters such as cutting speed, feed per tooth and radial depth of cut and each with three levels, and varied as a single-factor variable, and results were compared to dry and conventional MQL cutting. Subsequently, UMQL effectiveness is evaluated in terms of cutting forces, temperature, surface integrity (average surface roughness, 3D surface topography and surface texture) and chip morphology. The experimental results indicated that UMQL exhibited 18 %, 48 %, and 50 % reduction in milling forces, temperature and surface roughness compared to dry and MQL, respectively. Furthermore, in terms of topography and surface texture, UMQL produced relatively less peaks and valleys with more uniform surface features showcasing better heat and friction management at the machining zone due to its superior cooling, lubrication and chip flushing characteristics. Finally, the chip formation was studied in different environments, and UMQL showed the least number of friction tracks with uniform folds and minimal serration. Overall, the results indicated that UMQL provided the best performance regarding machinability, by forming a stable tribo-film with droplets effectively penetrating the cutting zone. Lastly from this study, the manufacturing industry will gain valuable insights into how certain cutting processing parameters and efficient lubrication will impact the mechanical behaviour in machining AISI 9310 parts and will offer a valuable resource for engineers and researchers to enhance machining processes while reducing environmental impact and operational expenses.